^  op 


ued  June  10 


U.  S.  DKIWRTMKXT   OF  AGRICULTURE, 

BUREAU   OF   ENTOMOLOGY     CIRCULAR   No.  123. 

L.  O.  HOWARD.  Enlomologisl  and  Chief  of  Bureau. 


METHODS  OF  CONTROLLING  TOBACCO 

[NSECTS. 


A.  ('.  MORGAN, 

Agent  mn/  Expert. 


1(17(11  —  10 1 


WASHINGTON   :  GOVERNMENT  PRINTING  OFFICE   :    1B10 


BUREAU  OF  ENTOMOLOGY. 

L.  0.  Howard,  Entomologist  and  Chief  of  Bureau. 

C.  L.  Marlatt,  Assistant  Entomologist  and  Acting  Chief  in  Absence  of  Chief  . 

R.  S.  Clifton,  Executive  Assistant. 

W.  F.Tastet,  Chief  Clerk. 

F.  H.  Chittenden,  in  charge  of  truck  crop  and  stored  product  insect  i  /instigations. 

A.  D.  Hopkins,  in  charge  of  forest  insect  investigations. 

W.  D.  Hunter,  in  charge  of  southern  field  crop  insect  investigations. 

F.  M.  Webster,  in  charge  of  cereal  and  forage,  insect  investigations. 

A.  L.  Quaintance,  in  charge  of  deciduous  fruit  insect  investigations. 

E.  F.  Phillips,  in  charge  of  bee  culture. 

D.  M.  Rogers,  in  charge  of  preventing  spread  of  moths,  field  work. 
Rolla  P.  Currik,  in  charge  of  editorial  work. 
Mabel  Colcord,  librarian. 

Southern  Field  Crop  Insect  Investigations. 

\V.  D.  Hunter,  in  charge. 

W.  D.  Pierce,  R.  A.  Cushman,  C.  E.  Hood,  E.  S.  Tucker,  George  D.  Smith,  \V.  A. 
Thomas,  T.  E.  Holloway,  George  W.  Hood,  V.  I.  Safro,  Harry  Pinkus, 
engaged  in  cotton  boll  weevil  investigations. 

F.  C.  Pishopp,  J.  D.  Mitchell,  H.  P.  Wood,  R.  A.  Cooley,  W.  V.  King,  engaged 
in  cattle  tick  life  history  investigations. 

A.  C.  Morgan,  G.  A.  Runner,  S.  E.  Crumb,  engagedin  tobacco  insect  investigations. 
I ).  L.  Van  Dine,  engaged  in  sugar  cane  and  rice  insect  investigations. 
F.  C.  Pratt,  engagedin  cactus  insect  investigations. 

Wilmon  Newell,  T.  C.  Barber,  engagedin  Argentine  ant  investigations. 
ii 


Circular  No.  123. 


Issued  June  10,  1910. 


United  States  Department  of  Agriculture, 

BUREAU   OF  ENTOMOLOGY. 

L.  O.   HOWARD,   Entomologist  and  Chief  of  Bureau. 


METHODS  OF  CONTROLLING  TOBACCO  INSECTS. 

Bj    A    C    Morgan, 
.|i/.  nl  and  Expi  rt. 

INTRODUCTION. 

[investigation  by  the  Bureau  of  Entomology  of  the  United  States 
Departmenl  of  Agriculture  of  insects  affecting  tobacco  has  been  in 
progress  in  the  "dark  tobacco"  districts  of  Kentucky  and  Tennessee 
since  Jubj  .  I  907. 

In  the  work  in  Tennessee  the  Bureau  of  Entomologj  has  had  (lie 
heartj  cooperation  of  the  Ten- 
nessee agricultural  experiment 
station  and  of  its  director,  Prof. 
II.  A.  Morgan.  During  the  sum- 
mers of  1908  and  1909  Professor 
Morgan  assigned  a  student,  Mr. 
I).  ('.  Parman,  of  the  University 
of  Tennessee,  a-  an  assistant  to 
the  Federal  agenl  in  charge  of 
the  tobacco-inseel  investigations. 
The  writer  wishes  to  express  his 
thank-  to  Professor  Morgan  for 
t lie  persona]  advice  received  from 

him  and  for  this  valuable  COOpera-      Fio.l.  -Agrotis  ypsilon,  one  of  the  tobacco  cut- 
jj(,ll  worms:  n.   Larva;  '<.  head   of  same;   c,  adult. 

.         .  ,,      •  Natural  size.    (From  Howard.) 

In  tin-  investigation  all  in- 
sects found  affecting  tobacco  have  Keen  studied,  hut  particular 
attention  has  been  given  to  the  differenl  species  of  cutworms,  to 
the  tobacco  flea-beetle  (Epitrix  parvula  Fab.),  and  to  the  tobacco 
hornworms  [PldegetTiontius  sexta  Joh.  and  /'.  quinqu*  maculata  Haw.). 
In  this  particular  circular  only  the  insects  mentioned  above  are 
considered.     Although    the    investigation   has  not    been  completed, 


METHODS    OF    COX  TROLLING    TOBACCO    INSECTS. 


it  is  thought  thai  a  description  of  remedies  already  in  use,  with 
the  addition  of  those  discovered  during  the  investigation,  may  be 
of  value  to  the  growers. 

It  should  be  stated  that  the  remedies  herein  treated  will  apply  not 
only  to  Kentucky  and  Tennessee,  but  should  apply  equally  as  well  to 
all  tobacco-growing  States  which  do  not  border  on  the  Gulf. 

CUTWORMS. 

Tobacco  is  frequently  very  seriously  injured  by  various  species  of 
cutworms,  of  which  two  common  species  are  illustrated  in  figures  1 

and  2.      It  is  the 


common  experi- 
ence of  all  farm- 
ers that  cut- 
worms are  the 
most  abundant 
and  injurious  on 
land  that  has 
been  left  uncul- 
tivated for  some 
t  iine  previous  to 
being  planted  to 
a  certain  crop. 
Where  tobacco 
follows  clover 
serious  injury 
from  these  pests 
is  likely  to  re- 
sult. On  the 
other  hand,  if 
winter  grain  pre- 
cedes tobacco  very  little  injury  is  likely  to  occur.  However,  if  tobacco 
is  to  follow  a  clover  sod  it  is  a  simple  matter  to  rid  the  soil  of  these 
"worms."  I  f  it  is  possible  to  do  so,  the  sod  should  he  plowed  under  in 
the  fall  or  winter  and  he  kept  free  of  vegetation  by  disking  orharrowing. 
Thus  by  keeping  the  held  free  of  vegetation  the  cutworms  will  be 
starved  to  death  before  the  time  for  setting  the  tobacco.  When  sod  land 
is  plowed  only  a  short-  time  before  setting  the  tobacco,  a  trap  bait  may 
be  used  to  rid  the  field  of  the  worms.  In  banners'  Bulletin  .No.  I20a 
Dr.  L.  O.  Howard  recommends  thoroughly  spraying  a  patch  of  weeds 
or  clover  with  Paris  green-,  then  cutting  it  and  dropping  it  in  little 
bunches  here  and  there  throughout  the  held.  Another  trap  bait  that 
meets  with  wide  favor  is  also  recommended  by   Doctor  Howard.''      It 


Fig.  2. — A  tobacco  cutworm  (Pcridroma  margaritosa):  <t.  Moth;  6,  normal 
form  of  larva,  side  \  i<s  w :  c,  same,  in  curved  position;  <2,  dark  formoi  larva, 
from  above;  e,  egg,  from  side;  f.egg  mass  on  twig.  All  natural  size  except  c, 
which  is  greatly  enlarged.     (  From  Howard.) 


"  Farmers'  Bulletin  X".  L20,  United  States  Department  of  Agriculture,  p.  'SA,  1900. 
6  Loc,  cit. 


METHODS   OF   CONTROLLING    rOBACCO    [NSE(    DS. 


consists  of  I  pound  of  Paris  green  mixed  with  50  to  75  pounds  of  bran, 
sweetened  with  molasses  and  moistened  with  water  to  make  a  mash. 
This  should  be  dropped  aboul  the  field  three  or  lour  days  before  the 
plants  are  set,  or  two  or  three  teaspoonfuls  should  be  dropped  about 
each  hill  after  the  plants  arc  set.  The  cutworms  are  very  loud  of  the 
sweetened  mash  and  will  generally  cat  it  in  preference  to  the  plants. 
[f  seed  beds  should  become  infested  with  cutworms,  the  bran  mash 
may  he  drilled  through  the  bed  and  the  ravages  of  the  worms  will  be 
stopped.  When  trap  baits  are  used  greal  'are  should  be  exercised 
in  keeping  all  live  stock  and  barnyard  fowls  out  of  the  field  until  the 
poisoned  materials  have  been  worked  into  the  soil. 

In  the  spring  of  1908  the  writer  applied  an  arsenate  of  lead  spray 
(made  at  the  rate  of  1  pound  of  arsenate  of  lead  in  paste  form  to  12 
gallons  n(  water  to  a  plant  bed  that  was  seriously  infested  with  cut- 
worms, with  the  result  that  all  the 
cutworms  were  killed  before  they 
had  done  any  appreciable  addi- 
t  ioiial  injury  tot  he  plants. 

THE  TOBACCO   FLEA-BEETLE. 
irir  parvula  I 

The  tobacco  flea-beetle  (Epitrix 
parvuhi  f'ah.)  (fig.  3)  is  known 
also  l>\  the  common  names  of 
"tobacco  Ilea"  and  "flea-beetle." 
It  max  be  found,  from  setting 
time  until  frost,  in  more  or 
less  injurious  numbers  in  evevy 
tobacco  held  in  the  I  'nitcd  States. 
The  most  injurious  outbreak  on 
record    occurred    in    the    ''dark 


Fio.  3.    Tin'  tobacco  flea-beetle  l  Epitrix  parmla): 
a,  Adult   beetle;  b,  larva,  side  view;  c,  head  of 
larva;  (/.hind  legot  same;  < .  anal  segment  of  same; 
/.  pupa.    «.  b,  i .  Enlarged  about  15  time 
more  enlarged,    i  From  Chittenden.) 


tobacco       distric 


of     Kentucky 

and  Tennessee  in  the  spring  of  1907.  Nearly  all  plant  beds, 
except  those  tightly  canvased,  were  devastated.  Practically  all  the 
first  sowing  was  destroyed  and  in  many  cases  the  second  and  third 
also.  I  n  consequence  t  he  acreage  \\  as  reduced  1  .">  to  '20  per  cent .  and 
owing  to  the  fact  that  the  crop  as  a  whole  was  set  much  later  than 
Usual  an  additional  loss  resulted.  Late-set  tobacco  docs  not  produce 
the  same  number  of  pounds  as  the  early-set  tobacco,  and  because  of 
l  he  lateness  of  harvesting  and  t  he  near  approach  of  cool  w  i 'at  her  this 
tobacco  frequently  cures  poorly  and  is  graded  lower  than  tobacco 
that   is  harvested  earlier  in   the  season.      The  loss  in   Kentucky  and 

Tennessee  in  1907  was  not  far  from  $2,000, - 

The  tobacco  flea-beetle  passes  the  winter  in  the  adult  stage  in  piles 
of  dead  leaves  or  dead  grass  in   the  woods,  or  in  fence  corners  and 


4  METHODS    OF    CONTROLLING   TOBACCO   INSECTS. 

similar  localities.  The  beetles  begin  to  emerge  from  hibernation  in 
Kentucky  and  Tennessee  in  March,  generally  about  the  time  the  young 
tobacco  plants  are  appearing  in  the  plant  beds.  The  young  and 
tender  plants  furnish  a  favorite  food  for  the  beetles,  and  unless  the 
beds  are  well  protected  by  canvas  considerable  damage  is  sure  to 
result.  The  flea-beetle  also  seriously  injures  tobacco  in  the  field. 
The  writer  has  observed  fields  where  numbers  of  plants  were  killed 
by  its  ravage-.  The  young  leaves  were  riddled  with  holes  (fig.  4  I  and 
new  foliage  was  completely  devoured  as  fast  as  it  appeared. 

The  tobacco  flea-beetle  occurs  upon  many  species  of  solanaceous 
plants,  as  it  has  been  found  feeding  upon  tomato,  potato,  horse  nettle, 
ground  cherry,  and  "jiinson  weed''  (Datura  stramonium).  It  lays  its 
eggs  on  or  near  the  base  of  the  stems  of  these  plants  and  also  upon 
the  stems  of  young  tobacco  plants.  The  principal  injury  to  tobacco 
is  occasioned  by  the  feeding  of  the  adults  upon  the  foliage,  although 


Fig.  -4. — Leaf  of  young  tobacco  plant,  showing  work  of  the  tobacco  flea-beetle.    (Original.) 

the  larvae  occasionally  do  considerable  damage  to  the  young  plants 
by  feeding  upon  the  roots  and  stems." 

PREVENTIVE    M EASURES. 

Properly  canvased  beds  escaped  uninjured  in  1907.  Only  whole, 
strong  canvas  should  be  u>ed,  with  boards  or  straight  logs  for  the 
sides  of  the  bed,  banking  up  the  earth  3  or  4  inches  againsl  the  sides 
so  that  no  holes  are  left  beneath  the  logs,  and  fastening  the  canvas 
closely  and  securely  to  the  sides.  Beds  canvased  in  this  way  will 
not  suffer  from  flea-beetle  attack. 

"  The  biology  of  this  insect  has  been  carefully  worked  out  by  Dr.  F.  II.  (  hittendeD 
in  Bulletin  No.  10,  of  this  office,  pp.  79  82,  and  in  Bulletin  No.  19,  pp.  85  87. 


Ml   CHODS    I  IF   CON  l  ROLLING    rOBACCO    [NSECTS. 


REMED1  VI.    MEAS1   IM  - 


Even  though  flea-beetles  do  gain  access  to  the  planl  beds  in  greal 
numbers  the}  can  be  controlled  economically.  Nearl}  all  the  severe 
loss  of  1907  could  have  been  averted  had  the  growers  known  the 
proper  remedy  to  apply.  The  writer  has  fun  ml  the  following  insecti- 
cide \ci-\  efficienl  in  killing  the  beetles  and  nol  at  all  injurious  to 
I  he  plants: 

Arsenate  of  lead  (in  paste  form,  or  \  pound  powdered  form  i. pound..  1 

Water " gallons.  .   L2  to  16 

Mix  the  arsenate  of  lead  thoroughly  in  a  small  quantity  of  water, 
pour  into  the  tank,  and  add  sufficient  water  to  make  the  desired 
ipiantit  \  ;  t  lien  apply  to  the  bed  with 
a  spray  pump  until  every  leaf  is  thor- 
ough!}      dampened.        Two       very      good 

spray  pumps  are  illustrated  in  figures  ."> 

and  •  >.  If  a  heavj  rain  falls  soon  after 
tlie  application  is  made  it  may  be  neces- 
sar}  to  make  a  second  application;  but 
it   must    be   remembered    that    arsenate 

Of    lead    will    stick    to     the    foliage    much 

longer  than  Paris  green,  and  will  nol  be 
greatly  dissipated  by  a  lighl  shower. 
After  tin'  plants  have  grown  consider- 
ably   it    will    he    tiece»arv    to    spraj    the 

bed  again  if  flea-beetles  are  still  numer- 
ous, for  the  new  foliage  will,  of  course, 
not  he  protected  by  the  first  applica- 
tion. 

If  flea-beetles  are  very  numerous  at 
the  time  of  setting  tobacco,  the  plant- 
can    he    protected     for    several    days    by 

dipping  the  tops,  just  before  setting,  in 
the  arsenate  of  lead  spray  recommended 

for  use  upon  t  he  plant  bed.  If  plant- 
are  not  dipped  at  setting  time  and  if  the 
flea-beetles  appear  in  the  fields  in  inju- 
rious numbers,  apply  the  arsenate  of 
lead,  in  the  strength  recommended  above,  with  a  knapsack  sprayer 
(fig.  •  '"■  With  I  hi-  sprayer  one  man  can  spray  from  o  to  li  acre-  of 
young  tobacco  in  a  day  at   a  COSl  of  from  25  to  •'!■">  cent-   an    acre    for 

arsenate  of  lead. 

Tobacco  growers  a-  a  rule  pay  too  little  attention  to  protecting 
their  plant  beds  from  insect  attack.     The  result  i-  that  more  of  the 


l-air  spray  pump. 


6 


METHODS   OF   CONTROLLING   TOBACCO   INSECTS. 


crop  has  to  be  set  late  than  would  he  the  case  if  the  beds  were  pro- 
tected. The  grower  should  always  be  prepared  to  fight  the  flea- 
beetle,  for  often  prompt  attention  to  insect  attack  upon  the  plant 
bed  will  enable  him  to  save  his  bed  and  thus  be  prepared  to  set  all 
his  crop  early. 

An  early-set  crop  of  tobacco  has  two  very  important  advantages 
over  a  late-set  crop.  The  first  is  the  production  of  a  better  grade 
and  of  more  pounds  to  the  acre,  as  mentioned  above.  The  second 
advantage  is  often  more  important  than  the  first.  An  early-set  crop 
will  frequently  mature  in  time  to  be  cut  before  the  August  "shower" 
of  tobacco  worms  is  large  enough  to  do  it  serious  injury.     This  point 

will  be  explained  more  fully  in  the  fol- 
lowing discussion  of  the  tobacco  horn- 
worms. 

THE  TOBACCO  HORNWORMS. 

(Phlegethontius    sexta   Joh.   and    Phlegeikontius 
quinquemaculata  Haw.) 

In  the  "dark  tobacco"  districts  of 
Kentucky  and  Tennessee  the  horn- 
worms  are  the  most  injurious  tobacco 
insects,  and  they  are  important  enemies 
of  this  crop  in  every  district  in  the 
United  States  where  it  is  grown.  There 
are  two  species,  the  northern  tobacco 
worm  (Phlegethontius  quinquemacuhta 
Haw.)  and  the  southern  tobacco  worm 
(Phlegethontius  sexta  Job.)  (fig.  7).  The 
northern  tobacco  worm  is  called  also  the  "Spanish  worm"  in  Tennessee 
and  Kentucky.  This  "worm,"  or  larva,  is  in  general  darker  than  the 
southern  tobacco  worm,  but  the  easiest  way  of  distinguishing  the 
two  species  is  by  the  white  markings  on  the  sides  of  the  body.  The 
northern  worm  has  S  V-shaped  markings  on  each  side  of  the  body, 
each  of  which  incloses  a  spiracle,  or  breathing  pore.  The  southern 
worm  has  7  oblique  lines  on  each  side  of  the  body,  each  of  which 
passes  in  front  of  a  spiracle. 

DISTRIBUTION. 

In  general,  as  the  common  names  indicate,  the  northern  worm 
is  most  numerous  in  the  north  and  the  southern  worm  is  most 
numerous  in  the  south.  The  northern  species  is  found  as  far  south  as 
Florida,  though  it  is  rare,  and  the  southern  species  has  been  collected 
in  Canada.  At  Washington,  D.  ('..  on  the  authority  of  Dr.  F.  II. 
Chittenden,  the  northern  species  predominates,  while  in  Tennessee 


Fig.  G. — Knapsack  spray  pump. 


Ml   CHODS    OF    CONTROLLING     COBACCO    [NSE<    is.  / 

the  southern  species  is  much  the  most  abundant.  These  two  species 
are  so  nearly  alike  in  their  work,  life  liiston  .  and  seasonal  history  thai 
the  remedial  measures  which  apply  to  one  will  apply  equally  well  to 
the  other.  The  life  history  and  seasonal  history  notes  given  in  tins 
article  are  from  observations  upon  the  southern  species  {Phlege- 
thontivs  sexto  Joh. 

LIFE    HISTOm     A\H    SEASONAL    HISTORY. 

This  circular  does  not  propose  to  describe  in  detail  the  life  history 
and  seasonal  history  of  the  tobacco  worms,  bul  to  give  only  such  data 


7.— The  Southern  tobacco  hornworni  {Phlt gelhonliv  \<lult;  6,  larva;  c,  pupa.    (From 

1  low  ard. 

as   are  necessary   for  the  proper  understanding  of   the    reasons   for 
recommending  cert  a  in  met  hoi  Is  of  control. 

The  tobacco  moths  begin  to  emerge  from  hibernation  about  June 
I.  and  in  a  few  days  more  t  he\  begin  to  deposit  eggs.  By  reference 
to  Talile  I  it  will  be  seen  thai  the  eggs  hatch  in  aboul  I  days,  and  thai 
the  "worms,"  or  larvae,  in  from  19  to  20  days,  pass  through  five  si  a 
of  growth.  They  t  hen  enter  the  soil  to  pupate  (fig.  8).  Those  thai 
pupate  not  later  than  the  last  week  of  .Inly  will  emerge  in  aboul  three 
weeks  as  adull  moths  of  the  second  generation,  and  will  commence 
10701     Cir.  I.'::  -10 2 


8  METHODS    OF    CONTROLLING    TOBACCO    INSECTS. 

depositing  eggs  in  3  or  4  days.  1  hose  that  pupate  after  the  10th  of 
August  will  usually  hibernate,  and  will  not  emerge  as  adult  moths 
until  the  following  year.     It  is  not  until  the  third  stage  of  growth — 


-   „-- 


Fig.  8. — Hibernation  of  Southern  tobacco  homworm:  c,  Pupa  in  hibernation 
cell  in  soil,  at  the  depth  al  which  pupation  usually  takes  place  in  the  stiller 
soils:  a,  cross  section  of  pupal  cell  viewed  from  below;  6,  pupal  cell  showing 
entrance  hole  of  larva  or  "worm."    Two-thirds  natural  size.    (Original.) 

that  is,  about  10  to  12  days  after  the  eggs  are  deposited— that  the 
larva' injure  tobacco  seriously.  In  the  fourth  (fig.  9)  and  fifth  stages 
one  larva  will  ruin  a  small  leaf  of  tobacco  in  a  single  day. 


METHODS    OF   <  ON  I  ROLLING    COBACCO    INSEi    I .-. 


Tabli    1        l      •"/'    lengt)  ig  lifi    history   of  tht    southern    U 

hornworm  (Phlegethontius  sexta). 


Emer- 

Illiitll 
tl>  l)V  i- 

Incu- 

[nstars,  01                    i           ol 

1 

Fourth 

Days. 

i 

Fifth. 

Total      p 

Din/s.       Days. 

1 

Days. 

3             3 

Days.      Dai/s.      Days. 
19.5            21             18 

^gr  'W 


; 


Larva,  fourth  instar.    Natural 


The  tobacco  moths,  as  has  already  been  stated,  begin  to  emerge 
from  hibernation  about  June  1 .  or  slightly  earlier,  and  the  errn  /</<  no 
continues  until  tin  middli  oj  August  or  later.  From  Table  1  we  sec 
thai  48  days  after  the  emergence  of  the  moths  from  hibernation  the 
hs  of  the  second  general  ion  will  become  adult ,  and  that  in  1  days 
more  they  will  begin  to  deposit  eggs.  These  eggs  will  hatch  in  I 
days,  and  in  6  or  7  days  more  thai  is.  in  about  t  wo  months  from  the 
emergence  of  the  first  moths  from  hibernation  the  larva?  of  the 
second  generation  will  pass  into  the  third  instar,  the  instar  in  which 
they  begin  to  injure  tobacco  seriously.  For  example,  let  us  take  I 
moths  thai  have 
emerged  from  hi- 
bernation    on    the 

following       dates: 

June  1 .  June  1 5, 
Juh  l .  and  July 
15.  The  second 
generation  of  to- 
bacco worms,  the  progeny  of  these  mollis,  will  begin  to  injure 
tobacco  seriously  aboul  August  1.  August  l">.  September  1.  and 
September  1  5,  respeel  iveh  . 

Although  moths  of  both  the  first  and  second  generations  are 
iting  i  jgs  during  late  Julj  and  in  August,  we  will  show  later 
thai  by  far  the  greater  percentage  of  them  has  just  emerged  from 
hibernal  ion.  and  belongs,  therefore,  to  the  firsl  generation.  This 
fad  has  a  very  important  bearing  upon  the  recommendation  of  fall 
plowing. 

Tobacco  worms  begin  to  enter  the  soil  to  pass  the  winter  (i.  e., 
hibernate  aboul  the  middle  of  August,  and  continue  doing  so  until 
Frost.  Usually  they  penetrate  the  soil  to  a  depth  of  from  :!  to  6 
inches.  Several  observations  upon  "second  bottom"  soils  of  the 
Cumberland  River  have  shown  the  average  depth  to  be  I  inches;  that 
is,  to  nearly  the  greatest  depth  to  which  the  land  was  plowed  in  pre- 

Noti       Fort!  this  article  the  date  of  oviposition  may  1 

taking  place  al  any  time  from  .tune  I  to  Jul)  15,  for  there  will  nol  be  a  second  genera- 
tion fi  ited  after  the  latter  date. 


10 


METHODS    OF    <  oXTROLLIXU    TOBACCO    INSECTS. 


paring  it  for  the  tobacco  crop.  After  the  larvae,  or  "worms,"  have 
reached  this  depth  they  twist  and  turn  many  times,  finally  forming 
by  this  action  oval  cells,  in  which  in  a  few  days  they  transform  to  the 
hibernating  form,  or  pupae  (fig.  8).  The  cells  protect  the  pupa'  much 
better  from  changes  in  the  weather  conditions  than  if  the  soil  were 
lying  in  close  contact  to  them.  The  insects  remain  as  pupae  in  the 
cells  during  the  winter  and,  as  has  been  stated,  begin  to  emerge  aboul 
the  1st  of  the  following  June  as  adult  moths  ready  to  deposit  eggs 
upon  tobacco. 

EMERGENCE    OF    THE    SOUTHERN    TOBACCO    HORNWORM     FROM     HIBERNATION. 

Careful  records  of  the  emergence  from  hibernation  of  the  moths  of 
the  southern  tobacco  worm  (Phlegethontius  sexta)  were  kept  during 
I  he  seasons  of  1908  and  1909  with  very  interesting  results.  In  1908 
the  emergence  began  about  the  last  of  May  and  continued  until 
August  13.  In  1909  the  emergence  began  June  1  and  continued 
until  August  22,  a  period  of  83  days.  The  records  of  1908  were  from 
an  emergence  of  58  moths.  The  records  of  1909  were  taken  from  an 
emergence  of  1,667  moths,  and  are,  therefore,  of  more  value  than  the 
records  of  1908.  The  most  interesting  part  of  the  data  is  the  fact 
that  in  both  years  a,  large  percentage  of  the  moths  issued  after  mid- 
summer. Table  II  shows  the  most  important  data  obtained  from 
the  emergence  records. 

Table  II. — Record  <>/'  i  im  rgi  nee  of  tobacco  moths  from  hibernation. 


i  vi  iod  "i  emergence. 

Emergence 
during 
period. 

Period  of  emergence 

Emergence 

during 
period. 

L908.o 

Per  ct  hi 
34.  5 
65.  5 
52 
63.8 

1909  ' 

l'ir  a  nt. 

J  J  7 

77.  :s 

Julv  21  in  July  31  .    . 

Julv  29  to   Vugusl  9 

50 

July  2]  In   i.UgUSl  1  3 

Julv  29  in   Vugus!    ! ' 

59 

i   ence  began  aboul  June  1. 


'•  Emergence  began  June  l 


From  Table  II  it  will  be  seen  that  there  was  a  large  wave  of 
emergence  in  1908  in  the  11  days  from  July  21  to  July  31,  inclusive, 
and  that  52  per  cent  of  the  total  emergence  took  place  during  that 
period.  The  record  further  shows  that  after  July  15,  5  per  cent  of 
the  total  emergence  took  place.  In  1909  the  results  were  very 
similar.  The  large  wave  of  emergence  took  place  during  the  1  1  days 
from  July  2!)  to  August  9,  inclusive,  and  77..'!  per  cent  of  the  emer- 
gence occurred  after  July  L5. 

REMEDIAL    MEASURES. 

It  has  been  the  belief  that  the  larger  percentage  of  the  tobacco 
worms  that  appear  in  late  July  and  in  Augusl  and  September  are  of 
the  second  generation.      This   is   not    true,   for  nearly  all   the  worms 


METHODS   OF   CONTROLLING    COBACCO    tNSECTS.  11 

that  appear  before  the  middle  of  J11I3  are  killed  by  hand  worming, 
ami  we  have  already  shown  In  means  of  the  life-historj  records  thai 
it  will  be  two  months  from  the  emergence  of  the  hibernating  genera- 
tion before  the  "worms,"  or  larvae,  of  the  second  generation  will  be 
large  enough  to  injure  tobacco  seriously. 

The  statement  has  been  frequently  made  to  the  writer,  and  personal 
observation  has  convinced  him  of  its  t  nidi,  thai  no  difficult}  is  experi- 
enced in  keeping  tobacco  free  of  worms  by  hand  worming  until  the 
middle  of  July  or  later.  Therefore,  if  tobacco  is  not  injured  by 
worms  until  after  the  middle  of  July,  the  conclusion  is  that  until  thai 
date  very  few  large  tobacco  worms  have  escaped  hand  worming  and 
that  the  second  generation  from  those  (hat  have  escaped  will  he  a 
very  small  one.  Byfartht  greater  portion  oj ''/n/wim  worms  that  appear 
in /uti  July  and  in  August  art  tht  offspring  of  moths  that  havt  emerged 
from  hibernation;  for  the  second  generation  of  worms,  the  offspring 
from  those  worms  thai  mature  after  July  15  will  not  be  of  sufficienl 
size  to  injure  tobacco  seriously  until  aboul  September  15.  If  tobacco 
has  been  set  early  the  crop  will  he  ready  for  the  barn  by  this  date 
and  will,  therefore,  escape  the  second  generation  of  worms. 

I   \  II      W  11    w  INTER    ri.ow  ING. 

Numerous  experiments  in  1907,  1  '.his,  and  L909  have  demonstrated 
that  as  a  rule  < >  1 1 1 \  aboul  one-fourth  of  the  tobacco  worms  that  hiber- 
nate are  able  to  survive  the  winter  and  become  adult.  A  part  of  the 
mortality  is  due  to  parasites,  bul  a  greater  pari  of  it  is  due  to  the 
unfavorable  weather.  'The  hibernating  period  is,  therefore,  a  verj 
critical  period  in  the  seasonal  history  of  the  tobacco  worm,  and  man\ 
of  those  that  do  survive  this  period  must  he  greatly  weakened. 
Hence,  an\  artificial  disturbance  ^>(  natural  conditions  will  produce 
an  additional  mortality.  As  has  been  stated,  the  hibernation  period 
is  passed  in  t  he  pupal  si  age  in  an  oval  cell  (fig.  8),  about  4  inches  below 
the  surface  of  t  he  soil. 

The  most  simple  met  hoi  I  of  disturbing  the  pupae  during  hibernation 
is  to  disk  or  plow  the  land.  Both  met  hods  were  t  rice  I.  It  was  found 
that  t he  disk  would  reach  onhj  from  5  to  111  per  cent,  of  t  he  cells,  and 
that  therefore  little  benefil  could  he  derived  from  that  treatment. 
II,  experiments  in  plowing  th<  land  kitted  mon  than  half  the  j>uj>:i 
that  would  otherwisi  havt  puss,,/  Hi,  winter  successfully.  The  ground 
should  he  plowed  to  the  same  depth  as  ii  was  in  preparing  it  for 
tobacco,  for  manj  of  the  tobacco  worms  will  go  down  to  the  hard 
soil  to  form  the  hibernating  cell,  that  i-,  to  the  greatest  depth  to 
which  the  soil  has  been  broken.  Plowing  will  throw  the  pupa'  and 
the  cells  up  to  or  near  to  the  surface,  will  break  the  cells  in  nearly  all 
Cases,   and    will    place    the    pupa'   in   close  contact    with    the   earth,    in 


12  METHODS   OF   CONTROLLING   TOBACCO   INSECTS. 

which  condition  they  are  most  susceptible  to  changes  in  temperature 
and  to  other  climate-logical  changes. 

A  week  or  ten  da}rs  should  elapse  between  the  time  of  cutting  the 
tobacco  and  the  plowing  of  the  land,  in  order  to  give  all  larva'  that 
are  in  the  soil  time  to  change  to  the  more  helpless  pupal  stage.  Plow- 
ing should  be  done  as  soon  thereafter  as  possible,  so  that  the  pupae 
will  be  exposed  as  long  as  possible  to  unfavorable  conditions. 

It  is  the  practice  in  many  localities  of  Kentucky  and  Tennessee  to 
disk  the  land  that  has  been  in  tobacco  in  preparation  for  the  wheat 
that  is  usually  sowed  after  the  tobacco  crop  has  been  harvested.  In 
some  localities  it  is  thought  that  disking  tobacco  land  is  a  better 
preparation  than  plowing,  for  the  reason  that  plowing  loosens  up 
the  soil  too  deeply  and  that  the  wheat  will  freeze  out  more  easily. 
Undoubtedly  this  may  be  true  for  some  soils,  that  is,  soils  that  con- 
tain little  clay  and  do  not,  therefore,  run  together  very  compactly. 
There  is,  however,  a  large  proportion  of  clayey  soils  in  the  Tennessee 
and  Kentucky  tobacco  regions  in  which  wheat  should  not  freeze  out 
easily.  In  fact,  many  farmers  always  plow  their  tobacco  land  in 
preparing  it  for  wheat  because  they  believe  they  obtain  a  better 
yield.  Whether  it  is  wise  or  not  to  plow  tobacco  land  for  wheat  is  a 
question  that  each  farmer  must  decide  for  himself.  But  it  is  certain 
that  plowing  will  cause  the  death  of  more  than  half  the  pupae,  while 
disking  will  kill  very  few.  Upon  the  looser  soils  it  would,  perhaps, 
be  better  to  change  the  rotation  and  to  sow  some  crop  other  than 
wheat  after  tobacco. 

COMBATING   TOBACCO   HORNWORMS    UPON    GROWING   TOBACCO. 

If  tobacco  is  planted  early  the  hand  worming,  necessary  to  kill  all 
worms  that  appear  before  the  large  emergence  wave  in  late  July 
(Table  II),  can  be  made  incidental  to  other  processes  in  the  growing 
of  tobacco,  and  will  require  very  little  additional  time  and  labor. 
Usually,  in  addition  to  the  cultivation  with  farm  implements,  tobacco 
will  receive  the  following  attention:  Two  hoeings,  hilling,  priming, 
and  topping,  and  much  of  the  early  tobacco  will  besuckered.  During 
these  necessary  operations  it  is  very  easy  to  discover  and  to  kill  the 
few  tobacco  worms  that  have  appeared,  but  when  the  large  wave  of 
emergence  appears,  hand  worming  will  be  found  very  costly,  and  in 
some  localities  impossible  because  of  the  scarcity  of  labor. 

When  tobacco  worms  are  numerous  it  will  require  an  outlay  of  at 
least  $8  to  $10  an  acre  to  hand-pick  (lie  worms,  and  frequently  the 
outlay  will  exceed  $10  an  acre. 

Us(  of  I'diis  green. — After  the  appearance  of  the  .Inly  and  August 
"shower  of  worms"  an  application  of  Paris  green  with  a  dust  gun 
dig.  10)  will  be  found  to  be  the  mosl  economical  means  of  combat. 
In  Tennessee  and  Kentucky  Paris  green  is  generally  applied  without 


.Mil  HODS    0]  ILLING     COBAI  I  0    INSECTS. 


13 


a  carrier,  but  the  writer  prefers  to  mix  ii  with  twice  its  weigh!  of 
finch  powdered  air-slaked  lime,  for  when  the  application  is  made 
without  a  carrier  the  cloud  of  dust  from  the  oozzle  of  the  dust  gun 
is  so  thin  thai  it  is  impossible  to  determine  whether  the  application  is 
being  made  evenly.  On  the  other  hand,  if  the  Paris  green  is  mixed 
with  aboul  twice  its  weighl  of  lime,  t  he  cloud  of  dusl  from  the  nozzle 
w  ill  alw  a\  s  show  whether  the  gun  is  working  properl)  .  and  a  clogging 
of  the  tubes  can  be  discerned  instantly.  Apply  flu  dust  early  in  the 
morning  '/7m//  tlu  dew  is  upon  thi  plants  and  when  that  in  no  h 


5  ^* -^^- -sr<^ 


10.— Applying  Pari  obaoco  with  a  dust  gun.    (Original.) 

Use  a  dust  gun  that  has  a  strong  fan  power,  and  apply  to  onlj  one 
row  at  a  time.  Greal  care  should  be  taken  to  make  the  application 
even  and  thorough.  No  definite  date  can  be  given  for  making  the 
Brsl  application.  The  time  will  depend  upon  the  appearance  of  the 
young  tobacco  worms,  and  it  may  be  the  last  week  in  duly  or  not 
until  aboul  the  middle  of  August.  In  1908  and  L909  some  of  the 
early  planted  tobacco  at  Olarksville,  Tenn.,  did  not  require  poisoning, 
and  in  L909  some  of  it  required  almost  no  worming.      The  first  appli- 


14  METHODS    OF   CONTROLLING   TOBACCO   INSECTS. 

cation  should  be  made  within  three  or  four  days  after  the  eggs  begin 
to  hatch.  A  thorough  application  of  from  three-fourths  of  a  pound 
to  1  pound  to  the  acre  should  be  sufficient  to  kill  the  young  larva1. 
Do  not  wait  until  the  worms  become  half  grown  before  making  the 
application,  for  in  addition  to  being  very  much  harder  to  kill  than 
the  young  ones,  they  will  do  considerable  damage  to  the  leaves  before 
the}  arc  killed.  In  dry  weather  a-  thorough  application  will  remain 
effective  for  a  week  or  ten  days,  but  if  there  is  a  rain  the  application 
should  be  repeated  immediately.  The  number  of  applications  and 
the  dosage  will  be  influenced  by  weather  conditions  whether  wet 
or  dry — by  the  numbers  of  young  worms  that  appear,  and  by  the 
earliness  or  lateness  of  the  crop.  By  watching  the  effect  of  an  applica- 
tion it  can  be  easily  determined  whether  it  is  losing  its  effectiveness 
and  whether  another  application  is  necessary.  The  presence  of  a  few 
large  worms  does  not  necessarily  mean  that  the  poison  is  ineffective. 
Some  worms  will  escape  the  most  careful  applications,  and  these 
should  he  hand  picked.  The  strength  of  the  later  applications  upon 
tobacco  that  is  nearly  grown  may  be  increased  to  1,  1^,  or  even  2 
pounds  to  the  acre. 

( 'aution.  --Do  not  apply  Paris  green  until  two  or  three  days  have 
elapsed  after  suckering,  for  if  a  light  rain  should  wash  the  Paris 
green  into  the  fresh  wounds  made  by  breaking  out  the  sucker,  the 
caustic  effect  of  the  free  arsenic  may  cause  the  leaves  to  drop  off: 
also,  do  not  apply  a  heavy  dose  of  Paris  green  to  tobacco  when  it  is 
beginning  to  "grain,"  for  the  leaves  are  then  more  susceptible  to 
"Paris  green  burn"  than  they  are  a  few  days  previous  to  "graining." 

Spraying  tobacco  versus  dusting. — In  this  circular  we  have  recom- 
mended dusting  tobacco  instead  of  splaying  for  two  reasons:  First, 
the  labor  of  spraying  is  very  much  greater  than  that  required  to 
apply  the  dust.  When  tobacco  is  nearly  full  grown,  that  is,  has 
begun  to  lap  in  the  row,  it  will  require  from  120  to  150  gallons  of 
water  to  spray  an  acre.  Therefore,  to  apply  the  spray  to  1  acre  a 
5-gallon  knapsack  sprayer  must  be  refilled  from  21  to  30  times. 
Second,  the  Paris  green  is  not  kept  in  suspension  very  easily  in  a 
knapsack  sprayer  and  the  last  of  the  spray  from  the  tank  is  likely  to 
contain  more  than  its  proportion  of  the  Paris  green  and  thus  cause 
injury  to  the  plant.  Furthermore,  if  great  care  is  not  used  in  apply- 
ing the  spiav,  a  part  of  the  plant  is  very  likely  to  be  drenched  and 
the  I'aiis  green  will  be  collected  along  the  midribs  and  in  the  axils 
of  the  leaves  in  sufficient  quantity  to  cause  serious  injury.  It  is  no! 
denied  (hat,  a  more  even  and  thorough  application  can  be  made  in 
spray  form,  but  with  negro  labor,  and  with  most  white  labor,  we  do 
not  believe  it,  will  be  made  as  satisfactorily  as  in  the  dust  form. 

Arsenic  left  upon  tobacco. — There  is  fear  among  growers  that  if 
arsenicals    are    used    a    sufficient    amount    of    arsenic    mav    be    left 


Ml   CHODS   ni     i'hxi  ROLL]  NG    I  OBA<  CO    [NSE<    I -. 


15 


upon  the  cured  tobacco  tt>  injure  the  user.  This  fear  is  groundless. 
Prof.  II.  Garman,"  state  entomologist  of  Kentucky,  reports  the 
results  of  several  experiments  to  determine  the  amount  of  arsenic 
left  upon  treated  tobacco.  Talis  green  was  used  at  the  late  of 
1  |  ic  n  i  in  I  to  1 60  gallons  of  water.  The  experimental  row  thai  received 
the  greatest  amount  of  Paris  green  received  8  sprayings  with  a  total 


11.—  Applying  Paris  green  to  tobacco  with  a  knapsack  spray  pump.    (Original.) 

of  I'  pounds  to  the  acre.  The  last  spraying  was  made  Augusl  22, 
and  the  tobacco  was  cut  September  I.  Analysis  of  this  tobacco 
showed  0.651  grain  arsenious  oxide  to  the  pound.  In  the  several 
experiments  performed  l>\  Professor  Garman  only  one  experiment 
gave  mimic  than  one  grain  of  arsenious  oxide  to  the  pound  of  dried 
tobacco,  and  the  tobacco  in  this  experiment  was  sprayed  the  daj  it 

Bui   63,  K>     \   i    I  up.  Sta  .  pp   69 


16  METHODS    OF    CONTROLLING   TOBACCO   INSECTS. 

was  cut.  Professor  Garman  concludes  that  very  little  danger  may 
be  apprehended  from  the  arsenic  left  upon  tobacco.  In  1909  the 
writer  made  several  experiments  to  determine  the  amount  of  arsenic 
left  upon  tobacco.  To  make  the  test  severe,  arsenate  of  lead  was 
used  because  this  arsenical  adheres  to  tobacco  much  longer  than 
does  Paris  green.  August  13  the  experimental  plat  received  a  spray- 
ing at  the  rate  of  5  pounds  to  the  acre,  and  on  August  18  a  second 
spraying  at  the  rate  of  4  pounds  to  the  acre.  Arsenate  of  lead  in 
dust  form  was  used,  hence  the  two  dosages,  amounting  to  9  pounds, 
were  almost  exactly  equivalent  in  the  amount  of  combined  arsenic 
to  Professor  Garman's  dosage  of  4J  pounds  of  Paris  green.  The 
tobacco  was  cut  September  8.  The  analysis,  made  by  the  Miscel- 
laneous Division  of  the  Bureau  of  Chemistry,  showed  an  average  of 
0.347  grain  arsenious  oxide  per  pound.  Heavier  dosages  of  powdered 
arsenate  of  load  left  only  0.501  and  0.531  grain  arsenious  oxide  per 
pound.  A  fatal  dose  of  arsenic  for  an  adult  is  about  two-thirds  of  a 
grain,  and  this,  of  course,  has  to  be  taken  into  the  stomach.  Since 
tobacco  is  not  taken  into  the  stomach,  and  since  so  little  arsenic 
will  be  taken  into  the  mouth  at  anyone  time, it  is  not  believed  that 
there  is  the  slightest  danger  in  using  tobacco  that  has  been  poisoned 
with  either  Paris  green  or  arsenate  of  lead;  in  fact,  the  writer  is  per- 
sonally acquainted  with  tobacco  growers  who  have  been  applying 
Paris  green  to  their  tobacco  for  from  six  to  eight  years  and  who  have 
been  chewing  and  smoking  the  cured  tobacco  without  injurious 
effects. 

POISONING   THE    TOBACCO    MOTHS. 

The  custom  of  poisoning  "  jimson"  blooms  with  arsenide  of 
cobalt  (flystone)  to  kill  the  tobacco  moths  when  they  feed  has  long 
been  recommended  and  has  been  practiced  in  nearly  every  tobacco 
region,  but  unfortunately  the  custom  has  fallen  into  disuse.  This 
method  of  combating  tobacco  moths  should  be  revived,  for  the  kill- 
ing of  one  female  moth  at  "  jimson"  blooms  will  be  equivalent  to  the 
killing  of  several  hundred  worms  later. 

The  following  is  the  formula  for  this  poison: 

Arsenide  of  cobalt  I  flystone) ounce. .      1 

Water pint.  1 

Sweeten,  just  before  using,  with  molasses  or  honey.  Place  a  few 
drops  in  each  bloom  late  in  the  afternoon. 

SUMMARY. 

CUTWORMS. 

1.  Plow  sod  land  in  the  fall  in  preparing  it  for  tobacco  and  keep 
down  all  vegetation  during  the  winter  and  spring.  This  will 
starve  the  cutworms. 


MKI  HODS   OF   CONTROLLING    COBACCO    tNSE(    CS.  17 

2.  [f  sod  land  has  no!  been  treated  as  recommended  above,  use  the 

poisoned  bail  four  or  five  days  before  setting  tobacco,  or  drop 
the  bait  aboul  each  lull  directrj  after  setting  tobacco. 

FLEA-BEETLES. 

3.  Canvas  seed    beds   tightly   with  strong  whole  canvas  and   thus 

prc\  cni  cm  l  \  of  i  he  beel  les. 
I.  Spiay  infested  l>e<ls  with  arsenate  of  lead  at  the  rate  of  1  pound 

paste  form  (or  J  pound  powdered  form)  to  12  gallons  of  water. 
5.   II'  flea-beetles  are  very  numerous  at  setting  time  dip  the  tops  of 

the  plants  in  tlu>  arsenate  of  lead  recommended  in  No.  4. 
(i.   [f  flea-beetles  continue  to  injure  plants  after  setting,  spray  with 

arsenate  of  lead  at  the  strength  given  above. 

n  Hi  \(  (  <  >    lloKN  W  OHMS. 

7.  Nearly    all    the    destructive    late   July    and    Augusl    "shower"    of 

worms  is  the  direct  offspring  of  tobacco  ninths  thai  have  issued 
from  hibernation  during  late  July  and  early  Augusl . 

8.  Over  60  per  cent  of  the  hibernating  generation  of  ninths  emerge 

from  hibernation  late  in  July  and  in  August. 

9.  Fall  plowing  of  land  that   was  in  tobacco  during  the  year  will 

destroy  more  than  half  of  the  hibernating  generation  ami  will 
thereby  reduce  proportionately  the  Dumber  of  tobacco  worms 
that   will  appear  the  next  year  late  in  July  ami  in  August. 

in.   Poison  worms  upon  tobacco  plants  by  dusting  with  Paris  green. 

11.  Poison  tobacco  moths  In  placing  a  few  drops  of  arsenide  of 
cobalt  (flystone    solution  in  "jimson"  blooms. 

Approved : 

.1  \mi>  Wilson, 

.s,  cretary  of  Agricultun  . 
Washington,  D.  ('..  April  is.  1910. 


UNIVERSITY  OF  FLORIDA 


3  1262  09216  5249 


